The application claims priority benefits under USC xc2xa7119 of Japanese Patent Application Serial No. 2000-67273, the disclosure of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission in which a roller is arranged in a toroidal cavity formed between an input disk and an output disk.
2. Description of Related Art
In this type of toroidal type continuously variable transmission, a plurality of groups of rollers whose positions are variable transmit a tractive force between corresponding raceway surfaces, parts of which are in a toroidal shape, formed on opposite surfaces of coaxial disks for input and output which rotate in opposite directions, as disclosed in JP-A-6-502476. The input disk and the output disk respectively have center holes through which an input shaft connecting with a power source is to be inserted. The input disk is connected to the input shaft so as to be integrally rotatable, and the output disk is supported on the input shaft so as to be rotatable.
The rotational speed transmitted from the input disk to the output disk varies when the position of the roller is changed. That is, when the roller is brought into contact with the input disk at a relatively high radius position, and is brought into contact with the output disk at a relatively low radius position, the output disk rotates earlier than the input disk, and a variator is set to a high gear ratio.
On the other hand, when the roller is brought into contact with the input disk at a relatively low radius position, and is brought into contact with the output disk at a relatively high radius position, the output disk rotates slower than the input disk, and the variator is set to a low gear ratio.
Generally, the roller is supported so as to be rotatable by a carriage extending in a direction perpendicular to its supporting shaft, and the axis of the carriage is inclined at a predetermined caster angle to a plane including a center circle of a torus.
Furthermore, the input disk and the output disk are urged in the direction nearer to each other by a hydraulic cylinder for disk urging. On the other hand, each of the rollers is urged in such a direction as to be pressed against the raceway surface of the disk by a corresponding hydraulic cylinder for roller urging through the carriage for supporting the roller.
Oil pressures respectively created by a lot of hydraulic cylinders, described above, are controlled, to apply a force to be balanced with a torque transmission force received by the roller to the roller through the carriage. Consequently, the angle of the roller varies such that a torque generated by the output disk is balanced with a torque generated by the input disk, to maintain the torques at a suitable ratio.
Actually, there is an inherent torque load received by the roller with respect to various types of combinations of various indispensable parameters (for example, a request by an operator, an engine load, an engine speed, and a final output speed). Accordingly, the control system receives inputs representing all the indispensable parameters, to set, when the torque ratio of the input disk to the output disk is suitably maintained, suitable oil pressure conforming to a torque reactive force received by the roller in each of the hydraulic cylinders.
As described in the foregoing, hydraulic cylinders for roller urging, whose number corresponds to the number of rollers, are required. Accordingly, the number of parts is large, and the amount of hydraulic fluid to be used is large.
Moreover, the number of sealing portions of the hydraulic fluid is increased. Accordingly, the possibility that oil leaks is increased.
Furthermore, friction produced when each of the hydraulic cylinders is operated is added. Accordingly, the friction is large as the whole of the continuously variable transmission, and hysteresis easily occurs in the operation of the continuously variable transmission. When the friction is further increased because seals of the sealing portions wear, the roller may vibrate due to the hysteresis.
The present invention has been made in view of the above-mentioned problems, and its object is to provide a toroidal type continuously variable transmission whose construction can be simplified and whose stable operation can be ensured.
In order to attain the above-mentioned object, a preferred mode of the present invention provides a toroidal type continuously variable transmission comprising an input disk supported on a rotating shaft so as to be integrally rotatable; an output disk supported on the rotating shaft so as to be relatively rotatable: at least one toroidal cavity formed between respective raceway surfaces of the input disk and the output disk; a group of rollers arranged in the cavity for providing for torque transmission to a portion between the input disk and the output disk which correspond to each other; a plurality of carriages for respectively supporting the rollers so as to be rotatable; means for connecting the plurality of carriages to one another; and a hydraulic actuator for collectively applying forces against torque transmission reactive forces respectively received by the rollers to the plurality of carriages through the connecting means.
In the present embodiment, a single hydraulic actuator can cope with the plurality of rollers. Accordingly, it is possible to reduce the number of parts and to simplify the construction. Further, the number of sealing portions is smaller, as compared with that in a case where a lot of hydraulic cylinders are used, thereby making it possible to significantly reduce the possibility that oil leaks. Further, friction at the time of the operation is small because the number of sealing portions is small. Even if the friction is somewhat increased because seals of the sealing portions wear by long-term use, the level of the friction is significantly smaller, as compared with that in the conventional example, not to cause the roller to vibrate.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.